High speed impact line printers comprise an endless type carrier band with a single row of characters moving parallel with a row of print hammers. The band is trained on spaced drive and idler or tension pulleys which are motor driven to revolve the band at constant speed. The band drive, as it is commonly called, is generally mounted on a support or frame member that holds the band in proximity to the row of print hammers mounted on another frame member. The hammers and the band are separated by a gap or throat which defines a passageway for a print medium such as paper forms and an ink ribbon.
The printing ribbon is sometimes a narrow strip wound on two widely separated spools with a section extending across the paper and lengthwise through the gap. Commonly the ribbon path is slanted relative to the line of the hammers and type band so that the entire width of the ribbon is presented for printing. Ribbon drive motors rotate the spools to feed the ribbon through the gap. Guide means between the spools is provided for maintaining the ribbon in proper alignment as it travels through the gap. The guide means necessarily are also widely separated to avoid interference with the hammer and paper feed operations and hence maintaining the ribbon on track presents a problem. The structures and arrangement of the guide means and the spool mountings have made it necessary to manually touch the ribbon when the ribbon is replaced and/or installed. The publication in the IBM Technical Disclosure Bulletin Vol. 31, No. 10, March 1989 pp. 32-33, shows a printer unit in which the type band drive is mounted on a frame above the horizontal paper path. A stretch of the ribbon between ribbon spools passes horizontally between the type band and paper. No guidance structure is shown. The ribbon spools are inserted into enclosures on either side of the paper path frame. Such an arrangement is not convenient because of space limitations if the print unit is located within a cabinet and the direction of paper feeding is from side to side instead of front to back.